01 / 32-148 / Initial Release / JCKasper / 06/20/2006
Functional Instrument Description
and
Performance Verification Plan
Dwg. No. 32-05002
Revision 01
June 20, 2006
Table of Contents
Preface 5
1 Introduction 6
1.1 The Cosmic Ray Telescope for the Effects of Radiation 6
1.2 Scope of this document 6
1.3 Outline of this document 6
1.4 Related documents 6
1.4.1 GSFC Configuration Controlled Documents 6
1.4.2 CRaTER Configuration Controlled Documents 6
2 CRaTER Overview 7
2.1 LRO Level 1 Measurement Objectives Relevant to CRaTER 7
2.1.1 RLEP-LRO-M10 7
2.1.2 RLEP-LRO-M20 7
2.2 CRaTER Level 2 and Level 3 Requirements 8
2.3 Overall Design 9
3 Telescope Design 11
3.1 Overview 11
3.2 Detectors 12
3.2.1 Detector Description 13
3.2.2 Thin and Thick Detectors 14
3.2.3 Detector Diameter and Maximum Event Rates 16
3.2.4 Leakage Current, Detector Noise, and Operating Temperature 18
3.3 Tissue Equivalent Plastic 19
3.3.1 Description and Composition 19
3.3.2 Use of TEP in CRaTER 19
3.4 Telescope Stack 20
3.4.1 Fields of Regard 20
3.4.2 Optimizing Fields of View and Geometric Factors 21
3.5 Telescope Board 23
3.6 Electronics Box 23
4 Electrical Design 23
4.1 Overview 23
4.2 Telescope Board 24
4.3 Analog Processing Board 24
4.4 Digital Processing Board 26
4.4.1 Test Pulse Generator 27
4.4.2 Low Level Discriminator 28
4.5 Power 29
4.5.1 DC-DC conversion 29
4.5.2 Bias Supplies 29
5 Measurement Process 30
5.1 Science Measurements 30
5.1.1 Overview 30
5.1.2 Description of Pulse Height Analysis 30
5.1.3 Internal Calibration Capability 31
5.1.4 Responding to Solar Energetic Particle Events 31
5.1.5 Primary Science Data Products 31
5.1.6 Secondary Science Data Products 32
5.2 Housekeeping 33
5.2.1 Overview 33
5.2.2 Variables Monitored 33
5.3 Commands 34
6 Instrument Requirements Verification Plan 37
6.1 Description 37
6.2 Level 2 Requirements Verification Matrix 38
6.3 Level 2 Requirements Verification Plan 39
6.3.1 CRaTER-L2-01 Measure the Linear Energy Transfer Spectrum 39
6.3.2 CRaTER-L2-02 Measure Change in LET Spectrum through TEP 39
6.3.3 CRaTER-L2-03 Minimum Pathlength through total TEP 39
6.3.4 CRaTER-L2-04 Two asymmetric TEP components 39
6.3.5 CRaTER-L2-05 Minimum LET measurement 40
6.3.6 CRaTER-L2-06 Maximum LET measurement 40
6.3.7 CRaTER-L2-07 Energy deposition resolution 40
6.3.8 CRaTER-L2-08 Geometrical factor 40
6.4 Level 3 Requirements Verification Matrix 41
6.5 Level 3 Requirements Verification Plan 42
6.5.1 CRaTER-L3-01 Thin and thick detector pairs 42
6.5.2 CRaTER-L3-02 Minimum energy 42
6.5.3 CRaTER-L3-03 Nominal instrument shielding 42
6.5.4 CRaTER-L3-04 Nadir and zenith field of view shielding 42
6.5.5 CRaTER-L3-05 Telescope stack 42
6.5.6 CRaTER-L3-06 Full telescope pathlength constraint 42
6.5.7 CRaTER-L3-07 Zenith field of view 42
6.5.8 CRaTER-L3-08 Nadir field of view 43
6.5.9 CRaTER-L3-09 Calibration system 43
6.5.10 CRaTER-L3-10 Event selection 43
6.5.11 CRaTER-L3-11 Maximum event rate 43
7 Glossary 44
Preface
Revision 01 of this document is being released for CDR.
1 Introduction
1.1 The Cosmic Ray Telescope for the Effects of Radiation
The Cosmic Ray Telescope for the Effects of Radiation (CRaTER) instrument is designed to characterize the lunar radiation environment on the Lunar Reconnaissance Orbiter (LRO) spacecraft. CRaTER will investigate the effects of solar and galactic cosmic rays on tissue-equivalent plastics as a constraint on models of biological response to radiation in the lunar environment.
1.2 Scope of this document
This Functional Instrument Description (FID) document provides an overview of the CRaTER instrument design as it took shape before the Critical Design Review in June 2006. The design described in this FID was developed to meet the requirements levied by the Level 2 through Level 3 requirements in the Instrument Requirements Document (IRD). The FID has two purposes, namely to describe the design that has been developed to meet the requirements levied in the IRD, and to present the procedures we have developed to verify that CRaTER meets the requirements.
1.3 Outline of this document
Section 2 presents an overview of the functioning of the instrument. Section 3 discusses the mechanical design. Section 4 covers the electrical design.
1.4 Related documents
1.4.1 GSFC Configuration Controlled Documents
· ESMD-RLEP-0010 (Revision A effective November 30 2005)
· LRO Mission Requirements Document (MRD) – 431-RQMT-00004
· LRO Technical Resource Allocation Requirements – 431-RQMT-000112
· LRO Electrical ICD – 431-ICD-00008
· CRaTER Electrical ICD – 431-ICD-000094
· CRaTER Data ICD – 431-ICD-000104
· Mechanical Environments and Verification Requirements – 431-RQMT-00012
· CRaTER Mechanical ICD – 431-ICD-000085
· CRaTER Thermal ICD – 431-ICD-000118
1.4.2 CRaTER Configuration Controlled Documents
· 32-01203 Contamination Control Plan
· 32-01204 Performance Assurance Implementation Plan
· 32-01205 Instrument Requirements Document
· 32-01206 Performance and Environmental Verification Plan
· 32-01207 Calibration Plan
· 32-02003.02 Mechanical Interface Document
· 32-02052 Analog to Digital Subsystem Electrical Interface Control Document
· 32-03001.01 Electrical Grounding Diagram
· 32-03010 Digital Subsystem Functional Description Document
· 32-04003.01 Reliability Assessment Document Drawing
· 32-04011.01 Analog Electronics Worst Case Analysis Drawing
· 32-05001 Detector Specification Document
· 32-05203 Electronics Subsystem Mechanical Interface Control Document
2 CRaTER Overview
NASA has established investigation measurement requirements for LRO based on RLEP Requirements and the LRO AO and refined further from the mission instrument selections and Project trade studies. In this section, the LRO Level 1 measurement requirements and rationales relevant to CRaTER are reproduced from Section 3.1.1 of ESMD-RLEP-0010, along with the associated product listed in Section 6.2 the instrument will produce in response to the LRO measurement requirements.
2.1 LRO Level 1 Measurement Objectives Relevant to CRaTER
2.1.1 RLEP-LRO-M10
2.1.1.1 Requirement
The LRO shall characterize the deep space radiation environment at energies in excess of 10 MeV in lunar orbit, including neutron albedo.
2.1.1.2 Rationale
LRO should characterize the global lunar radiation environment in order to assess the biological impacts on people exploring the moon and to develop mitigation strategies.
2.1.1.3 Data Product
Provide Linear Energy Transfer (LET) spectra of cosmic rays (particularly above 10 MeV), most critically important to the engineering and modeling communities to assure safe, long-term, human presence in space.
2.1.2 RLEP-LRO-M20
2.1.2.1 Requirement
The LRO shall measure the deposition of deep space radiation on human equivalent tissue while in the lunar orbit environment.
2.1.2.2 Rationale
The radiation environment needs to be characterized in order to assess its biological impacts and potential mitigation approaches, including shielding capabilities of materials and validation of other deep space radiation mitigation strategies.
2.1.2.3 Data Product
Provide LET spectra behind different amounts and types of areal density, including tissue equivalent plastic.
2.2 CRaTER Level 2 and Level 3 Requirements
Tabulated copies of the CRaTER Level 2 and Level 3 requirements listed in the IRD are repeated in this section for reference.
Item / Sec / Requirement / Quantity / ParentCRaTER-L2-01 / 4.1 / Measure the Linear Energy Transfer (LET) spectrum / LET / RLEP-LRO-M10
CRaTER-L2-02 / 4.2 / Measure change in LET spectrum through Tissue Equivalent Plastic (TEP) / TEP / RLEP-LRO-M20
CRaTER-L2-03 / 4.3 / Minimum pathlength through total TEP / > 60 mm / RLEP-LRO-M10, RLEP-LRO-M20
CRaTER-L2-04 / 4.4 / Two asymmetric TEP components / 1/3 and 2/3 total length / RLEP-LRO-M20
CRaTER-L2-05 / 4.5 / Minimum LET measurement / 0.2 keV per micron / RLEP-LRO-M10, RLEP-LRO-M20
CRaTER-L2-06 / 4.6 / Maximum LET measurement / 7 MeV per micron / RLEP-LRO-M10, RLEP-LRO-M20
CRaTER-L2-07 / 4.7 / Energy deposition resolution / < 0.5% max energy / RLEP-LRO-M10, RLEP-LRO-M20
CRaTER-L2-08 / 4.8 / Minimum full telescope geometrical factor / 0.1 cm2 sr / RLEP-LRO-M10
Table 2.2.1: CRaTER Level 2 instrument requirements and LRO parent Level 1 requirements.
Item / Ref / Requirement / Quantity / ParentCRaTER-L3-01 / 6.1 / Thin and thick detector pairs / 140 and 1000 microns / CRaTER-L2-01, CRaTER-L2-05, CRaTER-L2-06, CRaTER-L2-07
CRaTER-L3-02 / 6.2 / Minimum energy / < 250 keV / CRaTER-L2-01
CRaTER-L3-03 / 6.3 / Nominal instrument shielding / > 1524 micron Al / CRaTER-L2-01
CRaTER-L3-04 / 6.4 / Nadir and zenith field of view shielding / <= 762 micron Al / CRaTER-L2-01
CRaTER-L3-05 / 6.5 / Telescope stack / Shield, D1D2, A1, D3D4, A2, D5D6, shield / CRaTER-L2-01, CRaTER-L2-02, CRaTER-L2-04
CRaTER-L3-06 / 6.6 / Pathlength constraint / < 10% for D1D6 / CRaTER-L2-01, CRaTER-L2-02, CRaTER-L2-03
CRaTER-L3-07 / 6.7 / Zenith field of view / <= 34 degrees D2D5 / CRaTER-L2-01, CRaTER-L2-02
CRaTER-L3-08 / 6.8 / Nadir field of view / <= 70 degrees D4D5 / CRaTER-L2-01
CRaTER-L3-09 / 6.9 / Calibration system / Variable rate and amplitude / CRaTER-L2-07
CRaTER-L3-10 / 6.10 / Event selection / 64-bit mask / CRaTER-L2-01
CRaTER-L3-11 / 6.11 / Maximum event transmission rate / >= 1000 events/sec / CRaTER-L2-01
CRaTER-L3-12 / 6.12 / Telemetry interface / 32-02001
CRaTER-L3-13 / 6.13 / Power interface / 32-02002
CRaTER-L3-14 / 6.14 / Thermal interface / 32-02004
CRaTER-L3-15 / 6.15 / Mechanical interface / 32-02003
Table 2.2.2: CRaTER Level 3 instrument requirements and parent Level 2 requirements.
2.3 Overall Design
The two drawings in Figure 2.3.1 illustrate the overall mechanical design of CRaTER. The drawing on the left is of the entire assembled instrument. CRaTER consists of a rectangular electronics box with a tilted top cover (visible on the left) and a telescope assembly (visible on the right side of the first drawing and rendered in cross section in the drawing on the right).
Figure 3.2.1: Drawings of the CRaTER instrument. The image on the left is from CRaTER Mechanical Interface Document 32-02003.02 and shows the entire assembled instrument. The four electrical connectors all visible on the left side of the instrument, consists of the two redundant 1553 communications interfaces, temperature monitors to the spacecraft, and power from the spacecraft. The telescope assembly and the electronics box are assembled separately. The figure on the right is a cross-section of the telescope assembly, showing the stack of detectors and TEP, the connections between the detectors and their preamplifiers, and the single connector to the electronics box.
The electronics box houses a digital processing board (DPB) and an analog processing board (APB). The DPB interfaces with the spacecraft through the four connecters seen on the side of the instrument in the drawing on the left in Figure 3.2.1. From the left, there are redundant 1553 command and telemetry interfaces, feedthroughs for thermometers used for survival heaters and monitoring the instrument health by the spacecraft, and a connector for the spacecraft supplied 28V DC power.
The telescope assembly holds the telescope stack and the telescope electronics board (TEB). The TEB connects the telescope to the electronics box, delivers bias voltages to the detectors, and sends detector signals and calibration pulses through preamplifiers back to the APB. The preamplifiers are very sensitive, therefore it is desirable to limit electrical interference near the detectors. Therefore the telescope assembly is electrically isolated from the electronics box, and grounded on the same path as the signals from the preamplifiers to the APB. The telescope stack, visible in the cross section in the drawing on the right in Figure 3.2.1, consists of aluminum shields on the nadir and zenith sides to block low energy particles, followed by pairs of thin and thick silicon detectors surrounding sections of A-150 Tissue Equivalent Plastic (TEP).
Figure 3.2.2 is a functional block diagram of the entire instrument. It is based on the CRaTER reliability assessment and shows the critical components necessary for the functioning of the instrument. As described above, the telescope assembly houses the telescope stack and the telescope board. The electronics box assembly houses the APB and the DPB. The APB is described in detail in Section. It acts to shape the pulses from each of the detector preamplifiers, to further amplify the signals, and to generate calibration pulses for testing the response of each signal path. The DPB identifies and processes particle events and generates scientific measurements, controls power distribution within the instrument, records housekeeping data, and receives commands and sends telemetry to the spacecraft.
Figure 3.2.3: Block diagram of CRaTER showing the critical components of the instrument (Similar to reliability assessment drawing 32-04003.01). The telescope assembly consists of the telescope stack of detectors and TEP, and a telescope board with preamplifiers. The electronics box assembly consists of an analog processing board (APB) on which the pulses from the detectors are shaped and the digital processing board (DPB) which monitors the detectors for particle events, conducts the pulse height analysis, and tracks housekeeping data. The DPB also interfaces with the spacecraft through 1553 for telemetry, and receives a 1 Hz timing signal and 28V for power.
3 Telescope Design
3.1 Overview
In this section, we outline the physical construction of CRaTER, with a focus on the sensing portion of the instrument, or the telescope assembly. As described in the instrument overview in Section 2.3, CRaTER consists of two physical parts, the telescope assembly and the electronics box. The telescope is mechanically mounted to the electronics box, but the two structures are electrically isolated from one another. The entire telescope assembly is instead grounded to the digital signal ground. This is done to reduce noise on the spacecraft chassis ground reaching the detectors and the preamplifiers.
As specified in CRaTER L2 requirement CRaTER-L3-05 the telescope stack consists of components three pairs of thin and thick detectors surrounding two pieces of TEP. From the zenith side of the stack the components are the zenith shield (S1), the first pair of thin (D1) and thick (D2) detectors, the first TEP absorber (A1), the second pair of thin (D3) and thick (D4) detectors, the second TEP absorber (A2), the third pair of thin (D5) and thick (D6) detectors, and the final nadir shield (S2).
Figure 3.1: Cross section of the telescope assembly, showing the pairs of thin and thick detectors and the TEP in the telescope stack, and the associated telescope electronics board. A pigtail with signal and ground runs from each of the detectors to one of six preamplifiers on the telescope electronics board.
These components may be seen in Figure 3.1.1 below. Pairs of thin and thick silicon detectors are used to measure the LET spectrum. Section 3.2 reviews the detectors selected for CRaTER and discusses the need for the pairs of thin and thick detectors to cover the full range of LET possible in silicon. The three pairs are needed to cover the range in LET expected by SEP and GCR ions in silicon and after evolving through the TEP. Section 3.3 describes the A-150 Tissue Equivalent Plastic. Section 3.4 describes the optimization of the location of components in the telescope stack.